1. Field of the Invention
This invention relates to poly(phenylene ether)-polyester compositions which exhibit enhanced properties, such as improved flow.
2. Brief Description of the Related Art
Poly(phenylene ether) resins (referred to hereafter as "PPE") are commercially attractive materials because of their unique combination of properties, for example, high strength, dimensional and hydrolytic stability, and dielectric properties. Furthermore, the combination of these resins with polyester resins into compatibilized blends results in additional overall properties such as improved chemical resistance necessary for many automotive applications. Examples of compatibilized PPE-polyester blends can be found in U.S. Pat. Nos. 4,831,087, 4,927,881, 4,978,715, 5,096,979, and 5,212,255, which are all incorporated herein by reference. The properties of these blends can be further enhanced by the addition of various additives such as impact modifiers, flame retardants, light stabilizers, processing stabilizers, heat stabilizers, antioxidants and fillers.
The overall physical properties of compatibilized PPE-polyester blends would make them attractive for a variety of articles in the automotive market except that many of these articles are preferentially produced using conversion techniques such as injection molding. Some of the desirable applications, for example, exterior body panels have very long flow lengths and therefore require resins that have very low viscosities in order to completely fill the molding tools. Compatibilized PPE-polyester blends have inadequate flow properties at the processing temperatures that are needed to minimize the thermal degradation of the resins. Increasing the processing temperature to higher than these temperatures in order to reduce viscosity of the blends results in brittle parts and many surface imperfections in the final part, both of which are unacceptable.
Additives that increase the flow of other resin compositions are generally not useful in compatibilized PPE-polyester compositions as they typically either interfere with the compatibilization chemistry, or they act to improve the flow by lowering the molecular weight of one of the components of the composition, or they result in significant loss in the heat resistance of the composition. All of these results are unsatisfactory as one of the goals of the present invention is to improve the flow while retaining or enhancing the physical properties of the compatibilized PPE-polyester compositions.
It is therefore apparent that a long felt need exists for compatibilized PPE-polyester compositions that have improved flow yet retain the other attractive physical properties.